Abstract : Miraflores Dam spillway is a gravity ogee section designed for a maxiumum head on the crest of 18 ft. The spillway is composed of eight 45-ft-wide bays with veritical-lift gates. The spillway crest is at elevation 38.67 and the downstream face of the spillway is terminated by a 38-ft radius which brings the toe tangent to a horizontal plane at elevation -15. No stilling basin is provided. Since the spillway was put in operation in 1917 a maximum flow of 25,290 cfs has been experienced. This flow is about one-fourth of the spillway design flood. Erosion of the rock downstream from the toe of the spillway has progressed until the dam is in danger of partial failure. Model investigations on a 1:36-scale general model and 1:20- and 1:50-scale section models were made to determine the suitability of various schemes for protection against further erosion and for development of design details of the selected scheme. Results indicated that adequate protection would be provided by addition of a stilling basin consisting of a 40-ft-long apron terminated by a 3-ft-high dentated end still. (Author)